From a quick search on the firebird documentation, which almost made me believe that it wouldn't have a SUM() function, this seems to be close to what you need.

SELECT part.num ,

SUM(woitem.qtytarget) AS woitemqty,

LIST(wo.num, ',') AS wonums

FROM mo

INNER JOIN moitem ON mo.id = moitem.moid

LEFT JOIN wo ON moitem.id = wo.moitemid

LEFT JOIN woitem ON wo.id = woitem.woid AND woitem.typeid = 10

LEFT JOIN part ON woitem.partid = part.id

GROUP BY part.num, mo.id

On T-SQL, the concatenation could be something like this:

SELECT part.num ,

SUM(woitem.qtytarget) AS woitemqty,

STUFF((SELECT ',' + wo.num

FROM wo

INNER JOIN moitem ON wo.moitemid = moitem.id

WHERE moitem.moid = mo.id

FOR XML PATH(''),TYPE).value('.', 'varchar(max)'),1,1,'') AS wonums

FROM mo

INNER JOIN moitem ON mo.id = moitem.moid

LEFT JOIN wo ON moitem.id = wo.moitemid

LEFT JOIN woitem ON wo.id = woitem.woid AND woitem.typeid = 10

LEFT JOIN part ON woitem.partid = part.id

GROUP BY part.num, mo.id

The code might have errors because I can't test it without sample data.

EDIT: To understand the concatenation in T-SQL, check the following article: http://www.sqlservercentral.com/articles/comma+separated+list/71700/